The present invention relates to an ink jet recording apparatus, more particularly to an ink jet recorder having a recording head assembly using an ion drag pump system.
Usually, in the conventional ink jet recording apparatus, ink under pressure is ejected through an orifice to form an ink stream which ultimately breaks up into droplets. The ink droplets are formed by the periodic separation of the foremost portion of the ink stream which is ejected from the orifice. The ink droplets travel along a path toward a recording medium and are subjected to an electrostatic field to be deflected thereby in a selective manner. Thereby, only the ink droplets necessary for recording reach the surface of the recording medium, and the ink droplets not necessary for recording travel to a gutter and are collected. In many cases, the ink droplet deflecting means operates in conjunction with means which applies to the droplets an electric charge according to the desired amount of deflection for the droplet and the charged ink droplets then are caused to travel through a constant electrostatic field. The accurate control of deflection with such a system, however, depends greatly on the regular production of the ink droplets since this is critical to proper charging of the droplets. It is well known that, for this purpose, the mechanical vibration of a specified frequency is applied to the ink to control production of the droplets. In order to apply mechanical vibration to the ink, there are generally two measures adopted. According to one of them, a piezoelectric transducer is provided so as to surround the nozzle body of the recording head assembly coaxially. Such a nozzle is disclosed in U.S. Pat. No. 3,683,396 to Keur et al. U.S. Pat. No. 3,708,118 to Keur, or U.S. patent application Ser. No. 746,157, filed Nov. 30, 1976, assigned to Hitachi Ltd., assignee of the present application. In the ink jet recording apparatus using such a nozzle, the nozzle becomes large in size, and therefore, the responsiveness or controllability is not good. On the other hand, it is difficult to realize a recording head assembly of small size. The other measure adopted such apparatus is a nozzle in which the ion drag pump effect is utilized. Such a nozzle is described in e.g. The Review of Scientific Instruments, Vol. 39, No. 8 PP 1088-1089, in an article entitled "Production of Uniform Droplets by Means of an Ion Drag Pump". The present invention relates to an improvement of the recording head assembly of this type.